1. Field of the Invention
The invention concerns a procedure and a fixture for the heat sealing (jig welding) of foils along a weld joint or seal.
2. Description of the Background Art
Common fixtures of this kind, which are used in the packing industry to close foil bags, for example, are usually equipped with a sealing jaw that can be raised and lowered, extending crosswise over a conveying path on which the foil bags that are to be sealed are moved forward gradually. During each step of the process, the sealing jaw is lowered briefly onto the overlapping foil sheets that are to be sealed, and with the help of a resistance wire, or similar component, that runs in the sealing jaw in a longitudinal direction, the foils are heated briefly on the weld joint so that they are welded together or heat-sealed and, if desired, separated at the same time.
One disadvantage of these common fixtures consists of the fact that both the movable sealing jaws and the conveying device for the foil bag have to be moved gradually in cycle sequences that are adjusted to each other. With every work cycle a considerable amount of inert mass has to be accelerated and then slowed down again. This requires complex drive and control mechanisms. The dimensions of this fixture, overall mass of the movable parts, minimum lift of stroke of the sealing jaw and step size of the conveying device all increase with increasing packing size so that great design efforts are required, particularly when packaging larger size items, and only low productivity levels can be achieved due to correspondingly long cycle times.
Another disadvantage of common fixtures is the direct contact of resistance wires with the foil, easily causing operating failures due to contamination or the caking of foil material onto the sealing jaw. Particularly in the case of relatively long weld seams it is also very difficult to ensure even temperatures and contact pressures over the entire length of the sealing jaw and to obtain a weld joint of consistently good quality.